The person skilled in the art is familiar with various coloring systems for the provision of color-changing cosmetic agents, in particular for the skin or keratin-containing fibers such as human hair for example, depending on the requirements of the coloring process. In addition to oxidation coloring agents for permanent intense colors with corresponding fastness properties and coloring or tinting agents for temporary colors which contain substantive dyes as the coloring component, coloring agents are known which contain as dyes precursors of the natural hair dye melanin, from which nature-analogous dyes are developed through oxidative processes in the hair.
These colorings can take place under oxidation with atmospheric oxygen as the sole oxidizing agent, such that no further additional oxidizing agents need to be used. Such colorings are therefore particularly gentle on the hair structure. With repeated use in particular, the agents make it possible to restore the natural hair color of people with gray hair. However, the coloring capacities of the agents, with oxidization under atmospheric oxygen in particular, are in many cases unsatisfactory, requiring long contact periods or frequent repetitions of the coloring process.
Hair coloring agents based on dye precursors of the indole or indoline type are known from the publication EP-B1-1 098 627, which additionally contain an amino acid or an oligopeptide to improve colorings on gray hair. On blonde hair the colorings achieved all have an undesired red or blue tinge.
There is therefore a need for effective coloring agents based on nature-analogous dye precursors that form intense colorings even with atmospheric oxygen as the sole oxidizing agent. There also is a need for colorings that turn out with no undesired reddish, bluish or violet color shifts. In addition, there is a need for colorings that are long-lasting and develop quickly. Another object is moreover a reduction in the contact period and improved application of the hair color for the user. Furthermore, other objects, desirable features and characteristics will become apparent from the subsequent summary and detailed description, and the appended claims, taken in conjunction with the accompanying drawings and this background.